The long-term goal of this investigation is to understand the molecular mechanisms of morphogenesis of the inner ear and the associated congenital anomalies. The inner ear develops from the otic vesicle, formed by the invagination of a placode of cells, which in the current thinking, consists of a single cell type. This view is inconsistent with the recent findings in this laboratory indicating that a heretofore unrecognized population of cells, originating from the ventral part of the hindbrain neural tube, migrates into the otic vesicle. The contribution of these cells, termed as the Ventrally Emigrating Neural Tube (VENT) cells, to the development of the inner ear is completely unknown and its understanding is indeed the main goal of this study. The hypothesis to be tested in the study proposed here is that the VENT cells make specific contributions to the morphogenesis of the inner ear. The hypothesis will be tested in avian embryos by determining whether particular cell types or structures develop from the VENT cells and whether their failure to contribute causes specific defects in the inner ear, by using a variety of microsurgical techniques. Specific aims are: (1) Determine the cellular composition of the otic vesicle in quail embryos. (2) Determine the specific derivatives of each cell population of the otic vesicle. (3) Determine if the VENT cells are required for normal development of the inner ear. Results of this study should provide significant new information by indicating the specific derivatives and function of an additional cell population in the development of the inner ear, which would lead to a revision of one of our current concepts of inner ear development namely, all sensory organs and virtually all the cell types in the inner ear develop from a single cell type.